1. Technical Field of the Invention
The present invention relates generally to a starter which may be employed in starting an automotive engine, and more particularly to an improved structure of such a starter equipped with a planetary gear speed reducer working to reduce the speed of rotation of an electric motor and transmit it to an output shaft for cranking the engine.
2. Background Art
Japanese Patent First Publication No. 58-214668 discloses a typical engine starter equipped with a planetary gear train working as a speed reducer. The starter also includes a one-way clutch which has an outer in which support pins (also called planet gear pins) are installed to support planet gears of the planetary gear train rotatably and to which orbital motion of the planet gears is transmitted directly to transfer torque to an output shaft of the starter. The torque of the output shaft is transmitted to a pinion gear fitted on the output shaft slidably through a shift lever. The pinion gear is selectively brought into engagement with a ring gear to crank the engine. The starter further includes a partition plate and a thrust washer. The partition plate is disposed between the motor and the planetary gear train within a starter casing and extends in a radial direction of the starter casing. The thrust washer is of a typical flat shape and disposed between the planetary gear train and the partition plate.
After start-up of the engine, the pinion gear is returned backward through the shift lever along the output shaft and hits a wall provided on the output shaft. The impact arising from the hit is transmitted to the output shaft as a thrust load. The thrust load then acts on the planetary gear train through the one-way clutch (especially, a carrier of the clutch) and urges the planetary gear train (especially, the support pins and the planet gears) against the partition plate, which may result in wear of the partition plate. In order to avoid such wear, the thrust washer works to block direct transmission of the thrust load to the partition plate.
The thrust washer, however, undergoes rotational attraction arising from the rotation of the planet gears, thus resulting in mechanical noises. In order to eliminate such noises, a washer lock mechanism may be used, but it leads to a complicated structure of the starter. Engine vibrations usually cause an internal gear of the planetary gear train to vibrate in the axial direction of the starter. In order to absorb such vibrations of the internal gear, a wave washer or a rubber gasket may additionally be used between the internal gear and the partition plate, but it will result in an increase in total manufacturing cost of the starter.